1. Field of the Invention
The present invention relates to an intake air control device for an internal combustion engine, the device comprising a reed valve passage for supplying intake air via reed valves, to thereby prevent a back flow of intake air, and a sub intake passage for creating a swirl in a combustion chamber.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 58-210322 discloses an intake air control device comprising a reed valve passage in which reed valves are arranged, and a sub intake passage, for creating a swirl in a combustion chamber, having a control valve and bypassing the reed valves.
In the above intake air control device, when in a low engine speed and low engine load driving condition, the sub intake passage is opened by the control valve so that all of the intake air is supplied to the combustion chamber and passes through the sub intake passage, whereby a good combustion can be obtained by the creating of a swirl in the combustion chamber. When in a low engine speed and high engine load driving condition, the sub intake passage is closed by the control valve so that all of the intake air passes through the reed valve passage and is supplied to the combustion chamber, whereby a back flow of intake air is prevented by the reed valves and the control valve and it is possible to obtain a higher torque, to thus increase the charging efficiency.
In a high engine speed driving condition, a large amount of intake air is required, and therefore in the above intake air control device, the intake air is supplied to and passes through the reed valve passage in this driving condition. The reed valves are relatively large and are arranged in a reed valve passage having a large cross section, but a considerable pressure loss is generated when the reed valves are fully open to allow a large amount of intake air to pass therethrough, and thus a desired torque cannot be obtained and a sufficient amount of intake air is not supplied to the combustion chamber, and accordingly, a considerable pressure loss occurs.